The invention relates generally to matrix-addressed x-ray imaging panels, and more particularly, to a system for compensating for capacitively coupled artifacts and correcting an image signal generated by a matrix-addressed x-ray imaging panel.
Matrix-addressed x-ray imaging panels composed of amorphous silicon TFT and photodiode arrays have many useful applications in the fields of medicine and industrial inspection. Typically, solid state imaging systems use a two dimensional matrix, or photodiode array, to convert radiation into an image having an intensity proportional to incident radiant energy. In radiation imaging systems used in medical applications, radiation energy passing through, or emanating from, a patient's body is used for uninvasive in vivo visualization. An example of a high resolution solid state radiation imaging systems for such applications is exemplified by U.S. Pat. No. 5,340,988 assigned to the General Electric Company, the assignee of the instant application. Further, flat panel radiation devices that reduce phantom noise and image artifacts for improving resolution in such imaging systems are described in U.S. Pat. No. 5,610,404, also assigned to the General Electric Company.
An undesirable coupling known as capacitive coupling, also known as fringe capacitance, occurs between the photodiode electrodes and the data lines. As used herein, fringe capacitance is defined as the capacitance in a component or between a components and their connections other than the capacitance of a capacitor or capacitors.
This undesirable capacitive coupling degrades the performance of flat panel imaging devices. During some common imager operations the x-ray flux remains on during readout of the pixels. For example, in fluoroscopy imagers and imagers used in conjunction with radiation therapy, the radiation source is on continuously to maximize delivered dose, or is pulsed on periodically, resulting in radiation being incident on the detector array during the readout period. This simultaneous excitation and readout of the imager results in image artifacts or "phantom" images. The phantom images occur as a result of the fringe capacitive coupling between the respective photodiode electrodes and adjacent data lines. During the readout of a given photodiode attached to a given data line, the potential of the other photodiode electrodes, e.g., those associated with non-read pixels, continues to change as the radiation flux strikes the imager. The change in potential of the pixels not being read out is capacitively coupled into the data line, thereby inducing an additional charge which is read as part of the signal from the addressed pixel. This effect produces cross-talk or contrast degradation in the image, and is commonly evidenced in the display readout either as bright lines or dark lines (the latter having less "cross talk" than their neighbors).
Attempts to correct for the artifact caused by the additional charge, which degrades the quality of the image, have been made using a software correction algorithm. Such software, however, requires the total signal level on each data line to be known. If any region of the image is saturated, as frequently happens, then the total signal on each data line is not known and this software correction technique is less effective.
In order to obtain a high quality image, corrections must be made to the raw data obtained from the photosensor arrays to compensate for these effects. It is therefore seen to be advantageous that corrections be made to an image signal produced by a matrix-addressed imaging panel exhibiting capacitively coupled artifacts.